The Importance of Changes Observed in the Alternative Genetic Codes

The standard genetic code is a way of transmitting genetic information from DNA into protein world. The code is universal for almost all living organisms on Earth but small deviations have been observed for many cellular organelles and some specific groups of microorganisms with highly reduced genomes. Such modifications are called alternative genetic codes. There is no consensus about the factors that caused or allowed these changes. A popular concept assumes that the codes evolved under neutral evolution without adaptive constraints. In this paper we present findings that argue with such view. We examined the level of error minimization in amino acid replacements generated by the standard genetic code and its alternatives. We found that only 3 out of 23 tested alternative codes have worse quality than the standard genetic code. In agreement with that, many single codon reassignments observed in the variants of the standard genetic code are generally responsible for improving the quality of the codes under the studied criteria. These results indicate that the codon reassignments observed in the existing alternative genetic codes could play an adaptive role in their evolution to minimize translational and mutational errors. The study can help in designing alternative genetic codes for artificially modified organisms in the framework of synthetic biology.

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